1. Field of the Invention
This invention relates to prosthetic vascular access grafts. More particularly, this invention relates to multilayer composite vascular access grafts and their method of construction.
2. Description of the State of the Art
Vascular access is the method used to access the bloodstream for hemodialysis patients. Hemodialysis removes blood from the body and routes it to an artificial kidney machine where the blood is cleansed and returned to the patient. Hemodialysis patients require easy and routine access to the bloodstream. The most common forms of vascular access are an arteriovenous (A/V) fistula, a central venous catheter (CVC) for temporary access and a prosthetic vascular access graft (VAG). The A/V fistula generally takes 1 to 4 months after surgery to develop, and a CVC is generally inserted until the fistula is ready for use. A VAG is a synthetic tube that is implanted under the skin in your arm and connected to an artery and a vein. The VAG is the most widely used vascular access device for long term vascular access in the hemodialysis patient, since there are a variety of factors that prevent the use of an A/V fistula. More than 60% of the hemodialysis patients in the United States have a VAG.
Hemodialysis patients have benefited from high-flow cannulation VAGs for decades. A primary material used in the construction of a VAG is expanded polytetrafluoroethylene (ePTFE). The ePTFE graft has become a standard among vascular surgeons due to its high kink-resistance, conformability and biocompatibility. The primary disadvantage of the ePTFE graft is that it must be allowed to “mature” for at least two weeks after the implant procedure to ensure that sufficient tissue in-growth has occurred and, although not necessarily required, it is often hoped that cell endothelialization has occurred as well. This maturation time helps to provide hemostasis, long-term healing ability and patency to the graft.
Polyurethane VAGs have been introduced into the U.S. marketplace over the past three years and are beneficial in that they are available for cannulation immediately after implant, are self-sealing, and as a result, provide rapid post-cannulation hemostasis. There are a number of disadvantages with these grafts including undesired handling characteristics that make it difficult for the surgeon to create an anastomosis, particularly with smaller blood vessels. In addition, the high elasticity of polyurethane can result in pulling and kinking in the region of the anastomosis. Accordingly, one of skill in the art in the field of VAGs would benefit from the introduction of a VAG with improved performance characteristics, which include handling characteristics such as ease of suturing, kink resistance and the ability to serve as a cannulation route soon after the implant procedure.